Integrated circuits are fabricated on the surface of a semiconductor wafer in layers and later singulated into individual semiconductor devices, or “dies.” Since the material of a semiconductor wafer—commonly silicon—tends to be relatively fragile and brittle, dies are often packages in a protecting housing, or “package,” before the dies are interconnected with a circuit board. Packages may fall into any of a variety of package categories. Two such categories are exposed-die packages and non-leaded wirebond packages.
FIG. 1 shows a cross-sectional side view of an exposed-die package 100, such as a PowerPad® package or a plastic package. The package 100 comprises a die 102 coupled to a leadframe die pad 104 of a leadframe 106 by way of a die attach material 103 (e.g., epoxy). The die 102 is electrically coupled to the leadframe 106 using bond wires 108. The die 102, the bond wires 108, the die attach material 103 and portions of the leadframe 106 are encapsulated in a mold compound 110. The leadframe 106 comprises a plurality of leads 112 that protrude from the mold compound 110. At least some of the leads 112 may be electrically coupled to a circuit board 114. In this way, electrical signals are transferred between the die 102 and the board 114. Further, at least a portion of the die pad 104 is exposed from a surface 118 of the mold compound 110 and is in contact with the board 314. As such, heat is transferred away from the die 102 and toward the board 114 by way of the die pad 104. Thus, the board 114 acts as a heatsink for the package 100.
FIG. 2 shows a cross-sectional side-view of an exemplary non-leaded wirebond package 200 (e.g., quad-flat no-lead package, small-outline no-lead package). The term “non-leaded” connotes a lack of leads protruding from the package 200, as found in the package 100 of FIG. 1. The package 200 comprises a die 202 coupled to a leadframe die pad 204 of a leadframe 201 by way of a die attach material 203 (e.g., epoxy). The die 202 is electrically coupled to the leadframe 201 using bond wires 208. The die 202, the die attach material 203, the bond wires 208 and portions of the leadframe 201 are encapsulated in a mold compound 210. As previously mentioned, unlike the leaded package 100, the non-leaded package 200 does not comprise any leads. Instead, the die 202 trades electrical signals with a circuit board 214 by way of peripheral portions 216 (“peripherals”) of the leadframe 201. The peripherals 216 do not protrude from the mold compound 210 as do the leads 112 from the compound 110; instead, the peripherals 216 are exposed from a surface 218 of the mold compound 210. The die pad 204 also may be exposed from the surface 218. As such, because the die pad 204 is exposed from the surface 218 and is in contact with the board 214, heat is transferred away from the die 202 and to the board 214 by way of the die pad 204. Thus, the board 214 acts as a heatsink for the package 200.
In some cases, circuit boards coupled to such packages (e.g., boards 114 and 214) may have a design flaw or some other limitation that prevents adequate heat dissipation away from the package. In such cases, a device containing the circuit board may overheat and either be destroyed or thrust into a state of thermal shutdown. Some packages may comprise heatsinks coupled to the package mold compound (e.g., mold compounds 210, 310) to help dissipate heat away from the package. However, package mold compounds usually do not have adequate levels of thermal conductivity to compensate for the overheating effect described above.